Лако-красочные материалы — производство

Sandalwood oil is obtained by distillation of the parasitic tree Santa — lum album. The major components of the oil are the santalols (27, 28). Many syntheses of these and related chemicals have been reported but, elegant as they are, none compete economically with the oil itself. The synthetic sandalwood materials fall into two main classes, the so- called terpenophenols and the materials derived from campholenic aldehyde.

Addition of camphene or borneol to guaiacol gives a mixture of products. These vary in the nature of the terpene unit (since many rearrangements are possible) and in its position of attachment to the aromatic ring. Hydrogenation under high pressure produces an even more complex mixture. Hydrogenation leads to hydrogenolysis of one of the oxygen atoms and a variety of positional and conformational isomers of the resultant substituted cyclohexanol. In all, over 100 isomers are formed, but only two are thought to contribute to the odour; those with an isobornyl group attached to the З-position of the cyclohexanol in a trans configuration relative to the hydroxy group as shown in Scheme 4.33. The odour quality of the mixture depends on the exact balance of all of the components; and there are many products on the market with tradenames such as Sandela®, Sandel N®, Santalix®, Santalidol® and Indisan®.

Camphene

3-(Exoisocamphyl)cyclohexanols Scheme 4.33

Rearrangement of a-pinene oxide, catalysed by zinc chloride or bromide, gives a product known as campholenic aldehyde (Scheme 4.34). Aldol condensation of this with a second aldehyde or a ketone gives an a,/?-unsaturated carbonyl compound that can then be reduced

Scheme 4.34

to an allylic alcohol. Many materials of this type are on the market, some of which have also undergone further modification. Some tradenames, are Bangalol®/Bacdanol® (29), Brahmanol® (30), Sanda — lore® (31), and Polysantol® (32).

One unusual structure for a synthetic sandalwood is that of Osyrol®, which is produced from dihydromyrcene as shown in Scheme 4.35.

Diterpenes have, by definition, 20 carbon atoms in their structure. This means that very few are sufficiently volatile to possess an odour. One diterpene is used in perfumery because it and the derivatives concerned are odourless. That is, they are used as solvents. In view of their hydrophobicity and low volatility, these solvents also have fixative properties. Abietic acid is a major component of tall oil, the residue from distillation of turpentine. Esterification and hydrogenation pro­duces two solvents, as shown in Scheme 4.36.